CN108519679A - A Space Shaping Method of Ultrafast Laser Pulse Long Focal Depth - Google Patents

Abstract

The invention proposes an ultrafast laser pulse long focal depth space shaping method, which analyzes the output wavefront distortion caused by the photothermal effect of the microstructure shaping element, introduces a phase pre-compensation mechanism, and combines the laser transmission energy conservation law to study the axially convergent beam Aberration separation technology realizes precise control of laser input-output amplitude, phase and other parameters and phase division of shaping elements to maintain the beam convergence state within a long focal depth range. Study the influence of microstructure shaping element design and manufacturing errors on the output light intensity distribution, combine error correction and fast convergence technology, use ST improved phase design algorithm to improve iterative search efficiency, realize multi-order phase discrete approximation, and achieve high diffraction efficiency flat top The beam pulse energy space shaping modulation effect of square uniformly distributed light spots.

Description

A Space Shaping Method of Ultrafast Laser Pulse Long Focal Depth

technical field

The invention belongs to the field of laser shaping, and relates to an ultrafast laser pulse long focal depth space shaping method. It is used to improve the removal quality when engraving materials and reduce the influence of device surface irregularities.

Background technique

A new type of light source appeared in the 1960s, which has the characteristics of good monochromaticity, good directionality, good coherence, and energy concentration. Femtosecond optical pulses refer to laser pulses with a duration of 10 ^-12 s-10 ^-15 s. This laser pulse has the characteristics of extremely high peak power, wide spectral width and extremely short laser emission time. With its unique ultra-short duration and ultra-strong peak power, the femtosecond laser has created a new field of ultra-fine material, low damage and three-dimensional processing of materials, and its application is becoming more and more extensive. According to the ultra-short and ultra-intensive characteristics of femtosecond lasers, the applied research fields can be roughly divided into the research of ultra-fast transient phenomena and the research of ultra-intensive phenomena. They are all deepened and developed continuously with the shortening of laser pulse width and the increase of pulse energy. The most direct application of femtosecond pulsed laser is that people use it as a light source to form a variety of time-resolved spectroscopy techniques and pump/probe techniques. Its development directly drives the research of physics, chemistry, biology, materials and information science into the field of microscopic ultrafast processes, and creates some new research fields, such as femtosecond chemistry, quantum control chemistry, semiconductor coherence spectroscopy, etc. The combination of femtosecond pulsed laser light and nanoscopy allows the study of carrier dynamics in semiconductor nanostructures (quantum wires, quantum dots, and nanocrystals). In biology, people are using the differential absorption spectrum and pumping/detection technology provided by femtosecond laser technology to study the energy transfer, energy transfer and charge separation process of the photosynthetic reaction center. Ultrashort pulse laser is also used in the transmission, processing and storage of information.

The successful operation of the first desktop terawatt laser using chirped pulse amplification technology began in 1988. This achievement marked the beginning of femtosecond ultra-intensive and ultra-high-intensity photophysics research in the laboratory. In this field of research, since the effect of the ultrashort laser field is equivalent to or greatly exceeds the bound field of electrons in atoms, the perturbation theory cannot be established, and new theoretical treatments need to be developed. Under the light intensity of 1020W/cm2, the study of simulated astrophysical phenomena can be realized. Thermal electrons (200KeV) generated by ultra-high-intensity lasers of 1019-1021W/cm2. Another important application of femtosecond laser is microfine processing. Usually, according to the laser pulse standard, the laser pulse with a duration of more than 10 picoseconds (equivalent to the heat conduction time) is a long pulse. When it is used to process materials, the surrounding materials will change due to thermal effects, thereby affecting the processing accuracy. The femtosecond laser pulse with a pulse width of only a few quadrillionths of a second has unique material processing characteristics, such as a small or no melting zone in the processing aperture; it can realize a variety of materials, such as metals, semiconductors, and transparent materials. Even micromachining and engraving of biological tissues; the processing area can be smaller than the focal size, breaking through the diffraction limit, etc. Femtosecond lasers are currently being used by some automakers and heavy equipment manufacturers to process better engine fuel injectors. Using an ultrashort-pulse laser, holes a few hundred nanometers wide can be made in metals. At the recent Optical Society of America meeting in Orlando, IBM's Hayter said that IBM has used a femtosecond laser system for photolithography of large-scale integrated circuit chips. Cutting is performed with a femtosecond laser and there is almost no heat transfer. Researchers at Lawrence Livermore National Laboratory in the US have found that this laser beam can safely cut through high explosives. "The femtosecond laser holds promise as a cold-processing tool for dismantling decommissioned rockets, artillery shells and other weapons," said the lab's Rosk.

Femtosecond lasers can be used to cut fragile polymers without altering their important biochemical properties. Biomedical experts have used it as an ultra-precision surgical scalpel for vision correction surgery, which can reduce tissue damage without leaving surgical sequelae, and can even perform precision surgery on individual cells or be used for gene therapy. People are still investigating how femtosecond lasers can be used in dental treatment. Some scientists have discovered that the use of ultrashort pulse laser can remove a small piece of tooth without affecting the surrounding substances. The UMW series ultrafast laser micromachining workbench recently launched by Clark-MXR of the United States represents the most cutting-edge commercial femtosecond laser micromachining system in this field, which includes everything needed for micromachining with ultrashort pulse laser Equipment and accessories that can be used for micromachining any material to produce sub-micron fine structures without damage to surrounding materials, without material spatter, and with extremely precise and highly repeatable results.

An immediate application of femtosecond pulses is time-resolved spectroscopy. Use femtosecond pulses to observe ultrafast processes such as physics, chemistry and biology. Femtosecond pulses can be used as light sources for confocal microscopes to make three-dimensional images of biological samples. Optical coherence tomography (OCT) using femtosecond pulses as a light source can observe three-dimensional images of living cells. At this time, it does not use the time characteristics of femtosecond pulses, but the wide spectral lines of femtosecond light sources , to produce interference similar to white light, the reflection of phonons excited by femtosecond pulses in semiconductors can be used to measure the thickness of semiconductor films in real time, to monitor the growth of semiconductor films, and use femtosecond pulses for microfabrication, and the holes made are smooth There is no glitch, because the femtosecond pulse does not rely on thermal effect to melt and then evaporate, but directly evaporates the material by a strong field. The femtosecond pulse is used as a light source for optical communication, which can increase the existing communication speed by hundreds of times. High-energy The interaction between femtosecond pulsed laser and plasma can generate high-order harmonics and X-rays, which may be used in controlled nuclear fusion. People have also tried to use the terahertz radiation generated by femtosecond pulses to detect the packaging of integrated circuits. quality, and even the fat content of meat products. In conclusion, femtosecond pulses have many applications.

With the further development and improvement of femtosecond pulsed lasers, more application prospects will be opened up. It is worth noting that whenever the research develops to a certain stage, a group of researchers from various countries will separate from the research team to transform the research results into products. Of course, the original laser companies also pay attention to absorbing new research results.

In terms of national science and technology strategy, the US approach is to support several key universities and national laboratories, such as the Ultrafast Optics Center at the University of Michigan, the Strong Field Physics Laboratory at the University of California, San Diego, Lawrence-Livermore laboratory etc. Japan started the so-called "femtosecond technology plan" in 1996 in the form of a large-scale "production (industry) official (government, ie national laboratory) (university)" research project of the Ministry of International Trade and Industry. Well-known large companies, national laboratories and universities in the United States have also attracted Bell Laboratories in the United States to carry out research on femtosecond pulse technology, with the goal of becoming the leader in terabit high-speed communication technology.

In the field of femtosecond laser manufacturing, beam transmission positioning is very important to manufacturing accuracy and quality. The domestic Xi’an Institute of Optics and Mechanics has adopted the space beam flexible transmission technology and developed laser manufacturing technology and equipment for large-format complex patterns. However, manufacturing efficiency and stability Insufficient; Xi'an Jiaotong University has developed ultra-fast laser processing equipment for metal surface micro-texture, but the efficiency and practicability need to be improved; Dalian University of Technology uses laser and micro-cutting combined processing technology, which can only realize the surface pattern manufacturing of small-sized components; 510 Institute Leading the laser manufacturing of domestic spacecraft solid-surface antenna reflectors, but currently can only rely on Russian laser manufacturing equipment (expensive, nearly 10 million) and Xi'an Institute of Optics and Mechanics engineering prototypes, and the processing format, stability, and efficiency cannot meet the requirements; The technology and equipment for the marking of engine turbine parts are completely blank in China.

The laser engraving technology of large thin-walled milling parts of aero-engine casing is the core process of new aircraft engine manufacturing, which is related to the power performance of the engine. At present, the weight loss of aircraft is calculated in grams. Good prototyping technology is of great significance to the weight reduction of large aerospace components, but at present, there is no laser manufacturing equipment that meets the requirements for processing and engraving large aerospace components at home and abroad. For example, the LASERDYNE high-precision multi-axis laser processing system developed by the foreign PRIMA (North America) company has been used to solve processing problems such as laser engraving on the surface of thin-walled parts. The TORRESLASER laser engraving machine of M.Torres was integrated with the TORRESTOOL universal flexible fixture system for the first time, becoming the first engraving machine of the Airbus German factory. Up to now, foreign laser engraving equipment is mainly focused on one-time engraving of chemical milling parts, which can realize laser engraving of three-dimensional skin parts. Laser manufacturing equipment that meets the requirements of milling and engraving of thin-walled parts has not been manufactured in China. The CO2 laser engraving machine sold by Italy's PRIMA Company to my country's Liming Company can only complete the first engraving, and the price exceeds 10 million, but the engraving and weight reduction capabilities are insufficient.

The out-of-focus state in the process of ultrafast laser processing will affect the material removal quality of the engraving, and the irregular and small fluctuations on the surface of the device can cause the laser beam to deviate from the focus. It is necessary to develop a long-focus depth laser beam long-focus depth space shaping precision control technology. The present invention A space shaping method for long focal depth of ultrafast laser pulses is proposed to precisely control ultrafast laser pulses.

Contents of the invention

The out-of-focus state in the process of ultrafast laser processing will affect the material removal quality of the engraving, and the irregular and small fluctuations on the surface of the device can cause the laser beam to deviate from the focus. It is necessary to develop a long-focus depth laser beam long-focus depth space shaping precision control technology. The present invention A space shaping method for long focal depth of ultrafast laser pulses is proposed to precisely control ultrafast laser pulses.

When the conventional beam converges, the depth of focus is short, and the vicinity of the focus changes drastically. When engraving complex surface-shaped devices, high requirements are placed on the response speed of the mechanism, positioning accuracy, and structural stability. In order to ensure the consistency and uniformity of the engraved microstructure, it is necessary to study the axial beam shaping technology to achieve precise control of the beam convergence state over a long distance.

The traditional small-spot Gaussian beam scanning engraving method has low efficiency and poor uniformity. Therefore, it is necessary to study the space-time control technology of beam energy based on refraction and diffraction beam transformation, and shape the laser beam into a flat-topped square with uniform distribution to prevent sharp damage at the bottom and improve the roughness of the engraving surface. Spend.

The discretization of phase modulation data and the design and manufacture accuracy of shaping components determine the beam shaping effect at long focal depths. Therefore, it is necessary to carry out shaping-convergence experimental research to investigate the actual output effect of beam shaping, and iteratively correct iteratively to achieve the desired effect.

First of all, the laser light field control, phase segmentation algorithm and phase pre-compensation method are studied to realize the phase pre-compensation axial convergence beam phase difference separation technology of the long focal depth of the beam; then, the detection experimental optical path based on the liquid crystal spatial light modulation technology is built, and the monitoring simulation is obtained. Shaping the beam output effect of the phase data, studying the relationship between the shaping output and the design parameters, establishing the spatial output light intensity distribution and designing the feedback control model of each parameter (such as the number of sampling points, the size of the input and output surfaces, the size of the spacing, etc.), and correcting the effects of the output shaping effect Each parameter of the reshaping output is a long-focus square uniformly distributed focused spot.

An ultrafast laser beam long-focus space shaping method, which analyzes the output wavefront distortion caused by the photothermal effect of the microstructure shaping element, introduces a phase pre-compensation mechanism, and combines the laser transmission energy conservation law to study the aberration separation technology of axially convergent beams , to achieve precise control of laser input-output amplitude, phase and other parameters and phase division of the shaping element, and to maintain the beam convergence state in the long focal depth range. Study the influence of microstructure shaping element design and manufacturing errors on the output light intensity distribution, combine error correction and fast convergence technology, use ST improved phase design algorithm to improve iterative search efficiency, realize multi-order phase discrete approximation, and achieve high diffraction efficiency flat top The beam pulse energy space shaping modulation effect of square uniformly distributed light spots. Design the convergence-shaping detection optical path, experimentally analyze the phase data of the spot before and after the shaping and the change of the beam parameters; study the relationship between the shaping output and the design parameters, and establish the spatial output light intensity distribution and design parameters (such as: number of sampling points, input and output size, spacing, etc.) The feedback control model is used to modify the design parameters many times, so that the output results are closer to the theoretical simulation design results.

Detailed ways

An ultrafast laser pulse long-focus space shaping method, which analyzes the output wavefront distortion caused by the photothermal effect of the microstructure shaping element, introduces a phase pre-compensation mechanism, and combines the laser transmission energy conservation law to study the aberration separation technology of axially converging beams , to achieve precise control of laser input-output amplitude, phase and other parameters and phase division of the shaping element, and to maintain the beam convergence state in the long focal depth range. Study the influence of microstructure shaping element design and manufacturing errors on the output light intensity distribution, combine error correction and fast convergence technology, use ST improved phase design algorithm to improve iterative search efficiency, realize multi-order phase discrete approximation, and achieve high diffraction efficiency flat top The beam pulse energy space shaping modulation effect of square uniformly distributed light spots. Design the convergence-shaping detection optical path, experimentally analyze the phase data of the spot before and after the shaping and the change of the beam parameters; study the relationship between the shaping output and the design parameters, and establish the spatial output light intensity distribution and design parameters (such as: number of sampling points, input and output size, spacing, etc.) The feedback control model is used to modify the design parameters many times, so that the output results are closer to the theoretical simulation design results.

For those skilled in the art, the above-mentioned embodiments are only preferred embodiments of the present invention, and should not be understood as limiting the patent scope of the present invention. Under the premise of not departing from the concept of the present invention, some improvements and substitutions made belong to this invention. protection scope of the invention.

Claims (4)

1. An ultrafast laser pulse long-focus space shaping method for shaping laser light, including: measuring the output wavefront distortion caused by the photothermal effect of the microstructure shaping element, introducing a phase pre-compensation mechanism; combining laser transmission energy conservation The principle enables the aberration separation of axially convergent beams, and precisely regulates the laser input-output amplitude and phase parameters; performs phase division on the shaping element, and maintains the beam convergence state in the long focal depth range. 2. according to the ultrafast laser pulse long-focus space shaping method of claim 1, measure and draw the function curve of the influence of microstructure shaping element design and manufacturing error on the output light intensity distribution; Fit the function curve to obtain fitting function, combining the fitting function with error correction and fast convergence, using the phase design algorithm to improve the iterative search efficiency, and using the multi-order phase discrete approximation to perform beam pulse energy space shaping modulation with high diffraction efficiency flat-topped square uniformly distributed spots. 3. according to the ultrafast laser pulse long focal depth space shaping method described in claim 1, set up the convergence-shaping detection optical path, measure the light spot phase data and the light beam parameter change before and after shaping; measure and draw the relational curve of shaping output and design parameter, establish Feedback control model of spatial output light intensity distribution and design parameters. 4. The ultrafast laser pulse long focal depth space shaping method according to claim 1, modifying each design parameter at least twice, so that the output result is close to the theoretical simulation design result.